The IEEE1394 bus has become an important communication bus in the field of home systems. The IEEE1394 serial bus already provides an internationally standardized and very widely accepted bus for data exchange between terminals from both, the consumer electronics field, the precise designation of the afore mentioned standard is: IEEE standard for high performance serial bus, (IEEE) STD 1394-1995, IEEE New York, August 1996. In the year 2000 an improved version had been finalized with the reference IEEE1394a-2000.
The IEEE1394 bus is a wired bus and it is specified that a maximum of 63 stations can participate in the communication over the bus lines. The 63 stations can be distributed in an apartment or a house. The maximum distance between two stations is 4.5 m, however there are also existing solutions that overcome the distance limitation.
A problem with all wired bus systems is that a bus cable needs to be installed in every room where a bus station shall be located. This problematic gave rise to the wish of a wireless extension of the IEEE1394 standard. A stand-alone device or a cluster of devices shall communicate with a first cluster by means of a wireless link or bridge.
Today, wireless communication systems already exist that can be used for the wireless link/bridge. The document “Broadband Radio Access Networks (BRAN; Hiperlan/2; Packet Based Convergence Layer; Part 3: IEEE1394 Service Specification Convergence Sublayer (SSCS)” defines a sublayer emulating the IEEE link layer over an ETSI BRAN Hiperlan/2 wireless network. As such, it may be present in bridge devices between wired 1394 buses or in stand-alone wireless devices.
The inter-connection of the different buses (with different bus-ID's) involves an IEEE1394 bridge, which is currently under definition by the IEEE P1394.1 working group. Because of the use of different bus-IDs an application operating on bridges shall be bridge aware.
The box that connects the 1394 bus cable of a cluster to the is wireless bridge needs to have a standard conform 1394 inter-face but on the other hand it needs to have some additional functionality, which concerns the self-configuration phase of the network. The 1394 bus has life insertion capability and each time a device is added or removed from the bus a bus reset is performed. After a bus reset each bus node sends a self-ID packet to the bus, with which all other stations on the bus become aware of how many stations are present on the bus. The ID number is a 6-bit number so that 64 devices can be distinguished. There is a specific process defined in the 1394 standard, with which the ID numbers are assigned to the stations. This will be described in more detail later on.
For now it is sufficient to explain that this process will be done separately for both clusters that are connected through the wireless bridge. This is because the wireless bridge makes a bus reset isolation between both clusters. This is a problem and the customer would not accept a limitation in the control of bus stations due to the existence of two or more 1394 clusters in his home. The customer, therefore, wants to have a network topology being displayed in the form of one single cluster to be able to easily control the various devices from different locations. There is, therefore, the desire that all the stations in the network shall be configured as belonging to one 1394 bus and this calls for a modified self-configuration phase that must be performed in co-ordinated fashion in both clusters with the bridge circuit in-between.
The devices of the second cluster are not aware that they are connected via a wireless link to the network. To achieve transparent operation, it is necessary that the wireless boxes shall generate self-ID packets that reflect the topology on both buses.
A solution for this problem is already presented in the is European Patent Application 01 250 155.7 of the applicant. According to this solution, the physical layer circuit of the 1394 interface circuit for the boxes of the wireless bridge need to have an additional buffer memory in which the self-ID packet of the bus stations in the cluster, to which the wireless box is not connected, may be buffered. There is a process that transfers the self-ID packets of the bus stations in the cluster on the other side of the bridge over the wireless link after each bus reset.
A bottleneck of this solution is that different physical layer circuits need to be used in the boxes of the wireless link than in all the other bus stations of both clusters.
From the demands of modern production lines, it would be advantageous if the same physical layer circuit could be used in both types of bus stations regardless of whether they are part of the wireless link or not.